Inverse Model for Limited-Area Hindcasts on the Continental Shelf

Abstract

The authors have constructed an inverse model for interpreting subtidal velocity observations in a limited-area hindcasting context. The intended use is following removal of a best prior circulation estimate that accounts for tide, local baroclinicity, and the direct response to local wind forcing. The remaining, subtidal velocity signal is inverted to provide far-field subtidal pressure forcing. The forward portion of the model is a linearization of a full-physics 3D simulator (QUODDY). Its inversion is achieved by gradient descent, using an exact algebraic adjoint and strong dynamical constraints. The cost function is a weighted least squares blend of velocity mismatch plus boundary condition size, slope, and tendency. The control parameters are barotropic open-water boundary conditions. Solution is achieved in the time domain, as a complement to the frequency-domain ?detiding? inversion presented earlier. A simple test case is introduced to demonstrate features of the inversion: precision, accuracy, interpolation, and extrapolation. A representative application on realistic topography (Georges Bank) is given.